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Genetic Testing for Cancer: What You Should Know

Genetic testing, including the tests using the second generation sequencing technology, is becoming an very important tool to improve the quality of medical care to cancer patients and high risk population. But, unless the right testing is selected, the results of the gene sequencing won’t be able to help the doctors to take clinical actions that will benefit the patients.

In some cases, only a few genes are tested. For example, the BRCA1 and BRCA2 genes are tested for the risk of breast and ovarian cancer. In many other cases, multiple genes (a multigene panel) are sequenced to identify the mutated genes that drive the cancer’s growth and could be used as drug targets. In recent studies, scientists found out that multigene panel test has certain advantages over the single or double gene test to provide more clinical information in certain circumstances. Patients should talk to their doctors to know if a multigene panel test should be taken under their conditions.

Most of the gene sequencing test are performed on patients’ tumor samples obtained from the biopsy or surgery. As the procedure of pre-sequencing preparation of the samples is difficult to be standardized, the quality of gene sequencing result depends heavily on the depth of each sequencing test. Many currently available gene sequencing tests are performed only at the depth of 100 -250. According to the researchers, the sequencing test has to be at the depth of at least 500 to avoid missing important rare mutations in tumors, including those emerging mutations that may be indicative of drug resistance. Patients should ask their doctors if the gene sequencing tests prescribed to them will have a depth of at least 500 before getting the test done.